Rear differential cap/girdle...observation...

[FiveO]

In an effort to keep the site traffic up I wanted to share something...

Yesterday I had an Art Carr deep tranny pan installed...no problems at all. I also had a TA Performance rear differential girdle installed.

The Ford Racing/TA Performance rear diff girdle are basically the same...but the Ford Racing one is $30 more.

I got mine from Wes at Innovative Interceptors....great service!

The new rear girdle is an amazing piece of metal. Solid as all heck.

My observation:

The stock rear differential cap is like a piece of aluminum foil. I was absolutely amazed at how flimsy this thing is. I could probably bend it myself if I wanted to Its thin and very light.

If you get a set of new gears...or drag race at all....or even are an aggressive driver....get a new rear end differential cap.

I'll take some pics later and post 'em.

Total Cost:

$200 total (included $30 stud kit from www.innovativeinterceptors.com and 2nd day UPS).
$51 for fluid...3 quarts from local dealer: 75w 140, $17 a quart
$50 install at local shop

The shop guys were great. They didn't gouge me on install time and they even suggested I get the fluid myself and get it to them. Much cheaper as they have to mark it up if they provide it.

Great preventative modification for anyone pushing their car on occasion

[sailsmen]

Make sure they added the friction modifier to the rear end fluid or you won't have ltd slip.

[FiveO]

Make sure they added the friction modifier to the rear end fluid or you won't have ltd slip.

Yup...forgot to add that. I picked this up also.

[Dan]

Why is there a need for a strng diff cover on an on-raod vehicle? We upgrade these all of the time for four wheelng but I haven't heard the argument yet for road use.

I will admit, they are thin and light but they should never get the kind of abuse that it would take to bend one.

If I missed something please let me know.

Best,

Dan

[FiveO]

For normal everyday driving I'd say you don't.

For s/c'ed cars or someone whose N/A but pushing the vehicle I'd say the stronger rear end cover is a must.

There are actually two bolts that push up to the stud kit under the girdle and hold everything in place. Makes for a nice solid rear end...which is a good thing

Again...just my observations.

[SergntMac]

I will admit, they are thin and light but they should never get the kind of abuse that it would take to bend one. If I missed something please let me know. Dan

You use the word abuse, Dan, but I prefer enjoy. Nonetheless, mechanically speaking, the end results are the same.

Every mod suggested here will produce more power to the rear wheels, except tires. High performance tires increase the resistance to that power, and the differential takes the beating. The OEM differential and 8.8 assembly came from the Town Car limo, so, it's "heavier duty," yes, but never intended this kind of enjoyment.

Add to that, how MM owners tend to enjoy their MMs to a greater degree and something will give. The general advice given here, is that if your wants, needs and driving habits are in pursuit of more power and spirited driving, upgrade the rear end before it lets loose. When it does, it get expensive.

A few hundred bucks in preventive measures vs. a grand or more in rebuilding is a no-brainer IMHO. Take it from someone who blew it all apart, and learned the hard way. E-mail me at sergntmac@aol.com for pics.

[Dan]

Did you really blow apart your 8.8? What happened?

If you spun an axle housing in the carrier then I can understand this mod completely.

Please don't get me wrong. I am not against this mod. It is just that I am so familiar with the incredible strength of the 8.8 that I feel it would take a lot of HP to warrant the mod.

Axle girdles are a good mod. I will support them. I guess the question I don't know the answer to is how high your HP goes before you should start to consider one. I'll have to look into it a bit more. In the meantime, please detail what you did to your 8.8.

Thanks.

Best,

Dan

[Krytin]

My car is stock as far as HP, and I just had the carrier/posi and axles replaced (under waranty) @ 29k miles! It didn't grenade - but it was shot! I do "enjoy" my car every day!

[jstevens]

I agree that this may be overkill but I'm not that experienced. I don't mean to hijack your thread but I've read when you upgrade the gears to 4.10 or anything else you should change the differential. I don't really know what that means. I think it means making the posi stronger.

Thanks.

[FiveO]

I agree that this may be overkill but I'm not that experienced. I don't mean to hijack your thread but I've read when you upgrade the gears to 4.10 or anything else you should change the differential. I don't really know what that means. I think it means making the posi stronger.

Thanks.

I'd agree. Several members have upgraded to the Eaton Posi in the rear end.

Several have even blown the stock one.

[SergntMac]

I guess the question I don't know the answer to is how high your HP goes before you should start to consider one. I'll have to look into it a bit more. In the meantime, please detail what you did to your 8.8. Dan

Ummm...If you are asking me these questions, Dan, you have put a lot on my plate. Let's see what I can post to bore everyone to death...

Exactly why my rear end came apart, I can't say. I know the effect, but not the cause, and the effect was fatal to all the main components. The autopsy was not conclusive, not one single failure, but many. IMHO, something got loose and it failed like dominos after that. What went first, I don't know.

I still have the old parts, and I can see one ring bolt came apart and punctured the back cover. Another got jammed between the ring and pinion, and still another is burried in the differential case, cracking that too. Other ring bolts are missing, and the remaining are fused in place. Once ring teeth came off, it must have been a mixmaster of shrapnel in the oil, at least that's what it sounded like from behind the wheel.

Put a gun to my head and I'm still guessing. Bad ring bolts is the first obvious choice perhaps. OTOH, no ring bolt however sturdy can do it's job if the ring or pinion looses a tooth and jams into the gear set. All I can say is that the gear set is Richmond, and the ring bolts I recovered were not race quality.

The rebuild is entirely Ford Racing parts from the '03 catalogue.
Auburn differential # M-4204-A28
Ring and pinion # M-4209-G410
Stud kit # M-4034-A
Rear cover/girdle # M-4033-G
New bearings, case hardened ring bolts, and seals in one kit # M-4210-C
Friction modifier # M-19546-A
New OEM axles and outer bearings and seals, sorry I don't have the OEM numbers handy.

As for when this mod should be considered, Dan, I don't think anyone could tell you that by any HP/TQ scale alone. Even the highest HP/TQ won't harm an 8.8 if you set things up right, or, don't push it to extremes. Moreover, I believe even a bone stock MM has sufficient power to trash the rear end, it all depends on how your drive it.

IMHO, it's a matter of saving as much install and rebuild money as possible. This is why I caution others to plan their mods carefully, target quality, not cost. In other threads here, there is much discussion on rear end upgrade costs, and how much one should pay/allow in the budget. Remember, you get what you pay for, so, pick your wrench based on his quality, not his cost.

If it's me taking the rear end apart for a gear upgrade, it's simple math for me to figure out that it's cheaper to buy and install things like the stud kit and girdle now, rather than do it all again when a preventable failure occurs. IMHO, it never hurts to have some reassurance in place.

I do not challenge the inherent strength of the 8.8 either, Dan, it's known as reliable, sturdy and easy to work with. However, when you're attacking that reliability and strength from two directions, i.e. more power in and more resistance from improved traction, rear end weakness (if any) will come to the surface.

I agree that this may be overkill but I'm not that experienced. I don't mean to hijack your thread but I've read when you upgrade the gears to 4.10 or anything else you should change the differential. I don't really know what that means. I think it means making the posi stronger. Thanks.

IMHO, changing the differential is not necessary when upgrading the gear set. Anyone who says so, is spending your money foolishly. However, the FRP catalogue has a neat Traction-Lok upgrade kit (# M-4700-B) and it would not hurt to install that when tearing everything down, it's another half hour bench time. Again, preventive vs. repair.

In my situation, the differential case was also trashed, and a replacement was necessary. The aftermarket (Auburn, Eaton, Thorsen and so on) is cheaper than replacing the OEM stuff, and they are all within a few dollars of each other. They all perform to the same high quality standards too, so, which is best is exclusively a matter of personal taste. Hope this has been helpful, but it's just my .02c on the topic.

[FiveO]

Great info SergntMac....thank you.

[Dan]

Yes, GREAT INFO. Thanks.

I suspect that your failure was related to either the breakdown of a substandard part or the inccorrect installation of something. If I had to guess at the latter my guess would be an incorrectly torqued bolt.

I think that what I have learned here is that I will need to have my rear end opened and looked at something before 20K miles. That is less than 6K away for me right now. I'll probably do that during a rear diff fluid change with the next oil change.

Thanks for all of the info.

Best,
Dan

[SergntMac]

I suspect that your failure was related to either the breakdown of a substandard part or the incorrect installation of something. If I had to guess at the latter my guess would be an incorrectly torqued bolt. Dan

Six of one, half dozen of the other, Dan, I've considered all points of view here. And that's about where I left it too, thanks.

IMHO, the ring bolts were substandard, however, I likewise feel the same way about the gear set. Break off a tooth let that float around in the 75W90 until it whips itself up between the gears, and the best of ring bolts anywhere would fail, and with the violence I described earlier.

I think that what I have learned here is that I will need to have my rear end opened and looked at something before 20K miles. That is less than 6K away for me right now. I'll probably do that during a rear diff fluid change with the next oil change. Dan

Thank you again, Dan, this is good advice for anyone enjoying their MM as I do.

We don't discuss it much here and maybe that's because the MM is still relatively new, but our rear ends need as much attention and care as the tranny, so, think and act accordingly. Recovering a sample of your rear end lube for lab testing may be overkill, but at least get an eyeball on the largely ignored component of the MM drive train that works harder than others, and gets half our attention.

ALL Posi-Traction, Traction-Loc and Limited-Slip(TMs respected) differentials basically function the same way. It's a clutch based system that compresses metal on metal plates together to lock both axles under power, and release them with slip when called for. Mechanically, they are designed to slip in some conditions and IMHO, all differentials wear out, even from normal use. It's just a matter of mileage and enjoyment.

Like clutch failure on a stick shift car, some drivers get good mileage from the clutch while others do not, but none of them ever should really be surprised that a manual tranny clutch will someday need replacement. Fan belts wear out, brakes wear out, tranny clutches wear out, and yes, differentials wear out. If we were not so performance focused here, we would not notice (or, even care) if our Traction-Locs didn't...Anymore.

The reason I'm covering this again, Dan, is the posted comment about it being "necessary" to replace the OEM differential when you upgrade the gear set. Again, this is bad 411. IMHO...Rebuild when necessary, and replace with aftermarket when that cost reaches rebuild costs.

Whole differential assemblies from Auburn, Eaton, Thorsen and so on, are cheaper to purchase than fully rebuilding an OEM Traction-Loc differential from top to bottom. It's also easier, faster, and usually comes with other benefits as well. However, there is nothing wrong with the OEM Traction-Loc, not a thing. It can take all the enjoyment you can dish out, once you understand that it IS a component that needs attention from time to time. You can avoid having to choose between Auburn, Eaton, or, Thorsen with some forward thinking and preventive measures.

My advice to anyone considering a simple gear ratio change, is to have the OEM differential rebuilt with the Ford Racing 8.8 Traction-Lok kit, whether needed, or, not. Keep in mind that the major expense here is the gear change itself, so, adding the FRP kit (# M-4700-B) is only 50 bucks more in parts, and it comes with the friction modifier too. Don't forget the stud kit, or, the girdle, but add this all up, and upgrading the clutches seems cheaper here, even with the added 1/2 hour bench time once the differential is out of the car.

My advice to anyone having traction problems under warranty, and the fix is to rebuild/replace the OEM diff, go ahead and let L/M take care of that expense. But, consider slipping (excuse my pun) the wrench this FRP kit (and maybe buy him lunch too) just to buy yourself reassurance that you're not going to have to do this again soon.

BTW...The "big three" aftermarket differential manfacturers all now offer some kind of lock switching mechanism, be it electronic, magnetic, whatever...This is good development for them, but giving us a choice about when the differential should be locked, or, unlocked, is not good...Yet.

This option entices us to spend our mod money when we don't need too and honestly, as I read here, very few of us really know when to engage this feature anyway. Until we bring ourselves up to this level of understanding, and we all know exactly when it's good to be locked, or, good to be unlocked, this option does not belong in the hands of any MM driver. It's not a benefit to us...Again...Yet.

IMHO, not until I read some serious discussions of differential temps, differential lube, temp gauges on the dash and so on, having a diff lock switch on the dash may be ultimately dangerous. There are times the differential is better open, and times better locked, and until we share and agree on this 411, my advice is to leave it alone.

Again...Just more of my .02c.

[Dan]

Mac,

All good points. For many the rear end is more a mystery than the bottom end of the block. I am pretty familiar with them due to my other interest of 4X4 rock crawling. With us it is all "gears and rears."

Having a selectable locker is not as bad as one would think other than the driver needs to be smarter. The Jeep Rucicon, for example, comes with selectable lockers in each axle but you must be in lo range to use them and they will dissengage above 30.

I would be totally comfortable with a selectable locker that completely locks both axles together but if I mfgr'd a car I would want to make sure that there were many safeties built in.

Our cars already have the air compressor so installing an ARB (if applicable) would be a snap. Problem is that I don't need it at this point. Maybe after the S/C. Who knows?

I like your input and insite on this topic. You either knew a lot, learned a lot or both. When the tech goes to open up the diff in the rear I am going to make sure that I am there to watch the oil drain out and see what is sitting in the bottom of the diff.

I have a friend who sets up 4X4 gears about 3 times a week. Heck, I might bring it down to him just to have him eyeball it and measure it up at the same time.

Best,

Dan